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Atomistic observation on diffusion-mediated friction between single-asperity contacts


The field of nanotribology has long suffered from the inability to directly observe what takes place at a sliding interface. Although techniques based on atomic force microscopy have identified many friction phenomena at the nanoscale, many interpretative pitfalls still result from the indirect or ex situ characterization of contacting surfaces. Here we combined in situ high-resolution transmission electron microscopy and atomic force microscopy measurements to provide direct real-time observations of atomic-scale interfacial structure during frictional processes and discovered the formation of a loosely packed interfacial layer between two metallic asperities that enabled a low friction under tensile stress. This finding is corroborated by molecular dynamic simulations. The loosely packed interfacial layer became an ordered layer at equilibrium distances under compressive stress, which led to a transition from a low-friction to a dissipative high-friction motion. This work directly unveils a unique role of atomic diffusion in the friction of metallic contacts.

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Fig. 1: In situ TEM friction experimental set-up.
Fig. 2: The IL induced continuous sliding with low friction compared with the high friction without an IL.
Fig. 3: MD simulations of the interfacial structure and friction behaviour between W–Au asperities as a function of their relative distance.
Fig. 4: Low friction mediated by atomic diffusion in the loosely packed IL.

Data availability

All data needed to evaluate the conclusions in the Article are present in the Article and/or the Supplementary Information. Additional data related to this Article may be requested from the corresponding authors.

Code availability

The computational code used in this study is available upon request from the corresponding authors.


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S.X.M. acknowledges support from National Science Foundation (NSF CMMI 1824816) through the University of Pittsburgh. G.W. acknowledges support from National Science Foundation (NSF CMMI 1662615). C.W. was supported by the PNNL LDRD programme. This work was performed, in part, at the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by US Department of Energy, Office of Biological and Environmental Research and located at PNNL. PNNL is operated by Battelle for the US Department of Energy under contract DE-AC05-76RLO1830.

Author information




S.X.M. conceived the experiment. Y.H. carried out the TEM experiments under the direction of S.X.M. and C.W., D.S., Y.H. and X.W. analysed the data. Z.L. and G.W. performed the computational simulations and theoretical analysis. D.S., Y.H., X.W., L.Z. and S.X.M. wrote the manuscript. All the authors contributed to the revision of the manuscript.

Corresponding authors

Correspondence to Chongmin Wang, Guofeng Wang or Scott X. Mao.

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The authors declare no competing interests.

Additional information

Peer review information Nature Materials thanks Michael Moseler and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary information

Supplementary Figs. 1–9, Tables 1 and 2, and Video Captions 1–4.

Supplementary Video 1

In situ HRTEM observation of interlayer mediated low friction between W and Au asperities under low normal loads.

Supplementary Video 2

In situ HRTEM observation of interlayer mediated low friction between W and Au asperities under low normal loads.

Supplementary Video 3

In situ HRTEM observation of the high friction between W and Au asperities without the loosely packed interlayer.

Supplementary Video 4

In situ HRTEM observation of the metastable Au clusters resulting from the interlayer and their relaxation into ordered layers on the W asperity surface.

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He, Y., She, D., Liu, Z. et al. Atomistic observation on diffusion-mediated friction between single-asperity contacts. Nat. Mater. (2021).

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